CASP3 and hepatocellular carcinoma: The number of HCC cells in the G0/G1 phase of the cell cycle was increased by GYY4137, which was consistent with GYY4137 inhibition of cyclin D1, suggesting that cell cycle arrest of HCC cells was induced by exogenous H2S. GYY4137 promoted the cleavage of poly (ADP-ribose) polymerase (PARP) and upregulated the levels of cleaved caspase-9 and caspase-3 in HCC cells, suggesting that exogenous H2S induced apoptosis of HCC cells, which was consistent with the inhibition of GYY4137 on Bcl-2, survivin, and Mcl-1.